The present invention relates to novel 4-thio substituted coumarin derivatives and coumarin dimers, and processes for their preparation. The invention provides a synthetic process for the preparation of 4-thio substituted coumarin derivatives using mild reaction conditions, which provides a high substituent tolerance and is appropriate for use in solid phase syntheses for producing a library of 4-thio substituted coumarin derivatives for biological screening.
Strategies in new drug discovery often look to natural products for leads in finding new chemical compounds with therapeutic properties. One of the recurring problems in drug discovery is the availability of organic compounds derived from natural sources. Techniques employing combinatorial chemistry attempt to overcome this problem by allowing the high throughput synthesis and testing of hundreds or thousands of related synthetic compounds, called a chemical library. In designing the synthesis of a prospective therapeutic compound or a chemical library, one often looks to natural chemical motifs which are known to have broad biological activity. Of particular interest are materials which have structural components, such as coumarins, flavones, and isoflavones, which are similar to secondary metabolites from plant extracts.
Coumarins are widely distributed in the plant kingdom. Approximately 50 naturally occurring coumarin derivatives have been identified. Derivatives of coumarin posses a range of biological activities. Of particular interest to researchers are modification at the 3- and 4-position of the coumarin scaffold and synthesis of symmetrical and unsymmetric dimers of coumarin compounds for biological evaluations. To avoid confusion, the coumarin derivatives described herein are numbered according to the following convention: 
Unfortunately, the preparation of such coumarin derivatives has suffered from multiple difficulties. This is particularly true of 4-substituted thiol derivatives of coumarin. Although certain 4-thio coumarins have been prepared, their synthesis has involved harsh conditions (such as the use of stoichiometric amounts of strong bases or toxic reagents, often under high temperatures), multiple synthetic steps, and poor substituent tolerance. For example, Parfenov et al. discussed a route for synthesis of 4-coumarinyl sulfides derivatives from 4-tosyl coumarin using harsh reaction conditions or from 4-chloro coumarin, which was generated under acidic conditions and high temperature. Parfenov et al., Khim. Gererotsikl. Soedin., 1991, 8, 1032. It is known that the selectivity of the reaction of 4-hydroxycoumarin with chlorinating reagents such as PCl5 and POCl3 is low, because a considerable amount of 4-chloro-3,4,3xe2x80x2,4xe2x80x3-tercoumarin will be formed as a by-product. Also reported with regard to substituted 4-thio coumarin derivatives, is a paper by Martin Kov{haeck over (c)}, in ARKIVOC, 2001, part (vi), which utilizes 4-chlorocoumarin as an intermediate to synthesize 4-ethylthiocoumarin under basic conditions at elevated temperature (reflux) using sodium ethanethiol. Although a high yield of product was obtained by this methodology, it is not applicable to the production of a large variety of 4-thiol substituted derivatives with a diverse substitution pattern because of the harsh reaction conditions (both acidic and basic) used to arrive at the product. Extension of this route to solid supported synthesis for production of a combinatorial library is limited due to the acid sensitivity of many common solid support linkers.
The present invention is directed to certain 4-thio substituted coumarin derivatives of the formula I 
wherein
R1 is selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
R3 is selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or R3 is a group of the formula
Zxe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from H, xe2x80x94CO2R, xe2x80x94OR, xe2x80x94SR, xe2x80x94NR2, 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 0 and 1, provided that when a=0 then b=0, and when c=0 then d=0;
or R3 may occupy two adjacent positions to form a fused aromatic ring, n is selected from values between 0 and 4;
R5 is selected from hydrogen, lower alkyl, lower alkenyl, lower alkynyl, and lower aralkyl, each of which may be unsubstituted or substituted with one or more substituents selected from halogen, lower alkyl, and lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide; or R5 may be a group of the formula 
wherein
R2 is selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
R4 is selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or R4 is a group of the formula
Z-(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 0 and 1, provided that when a=0 then b=0, and when c=0 then d=0;
or R4 may occupy two adjacent positions to form a fused aromatic ring, and, m is selected from values between 0 and 4.
Therefore, the present invention provides for symmetrical and unsymmetrical dimeric forms of 4-thio-substituted coumarin derivatives of the formula II: 
wherein
R1 and R2 are independently selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
each R3 and R4 is independently selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or is a group of the formula
Zxe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 0 and 1, provided that when a=0 then b=0, and when c=0 then d=0;
or R3 or R4 may occupy two adjacent positions to form a fused aromatic ring, n and m are independently selected from values between 0 and 4.
The invention also provides for 4-thio coumarin derivatives of the formula III: 
wherein R1 and R3 and n are as described above for compound I.
The invention further provides for 4-thio coumarin derivatives of the formula X 
wherein R3 is as described for the compound of formula I,
R6 is selected from halogen, halogenated methyl, methoxy, and ethoxy;
R7 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy;
R8 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy, and
R9 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy.
The invention also provides a synthetic process for the preparation of compounds of the formula I. The process uses mild reaction conditions, which provides a high substituent tolerance. Thus, the process is applicable to the preparation of a wide variety of 4-thio substituted coumarin derivatives with diverse substitution patterns. Additionally, the process is appropriate for use with the solid-support (solid phase) synthesis of 4-thio substituted coumarin derivatives. Thus, the process provides a method for producing a library of 4-thio substituted coumarin derivatives for biological screening.
The term xe2x80x9chaloxe2x80x9d or xe2x80x9chalogenxe2x80x9d as used herein includes fluorine, chlorine, bromine and iodine.
The term xe2x80x9clower alkylxe2x80x9d as used herein contemplates both straight and branched chain alkyl radicals containing from one to six carbon atoms and includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and the like.
The term xe2x80x9ccycloalkylxe2x80x9d as used herein contemplates cyclic alkyl radicals containing form 3 to 7 carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, and the like.
The term xe2x80x9clower alkenylxe2x80x9d as used herein contemplates both straight and branched chain alkene radicals containing from two to six carbon atoms.
The term xe2x80x9clower alkynylxe2x80x9d as used herein contemplates both straight and branched chain alkyne radicals containing from two to six carbon atoms.
The term xe2x80x9cC2-C8 acylxe2x80x9d as used herein contemplates both straight and branched chain acyl radicals containing from two to eight carbon atoms and includes acetyl, propionyl, 2-methylbutyryl and the like.
The term xe2x80x9clower alkyl esterxe2x80x9d as used herein contemplates the straight and branched chain lower alkyl esters including xe2x80x94CO2CH3, xe2x80x94CO2CH2CH3, xe2x80x94CO2CH(CH3)CH2CH3, and the like.
The term xe2x80x9clower alkyl amidexe2x80x9d as used herein contemplates the straight and branched chain lower alkyl amides including 
and the like.
The terms xe2x80x9caralkylxe2x80x9d as used herein contemplates a lower alkyl group which has as a substituent an aromatic group.
The term xe2x80x9caromatic groupxe2x80x9d as used herein contemplates 5- and 6-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine, and the like. Those aromatic groups having heteroatoms in the ring structure may also be referred to as xe2x80x9caryl heterocyclesxe2x80x9d or xe2x80x9cheteroaromaticsxe2x80x9d. The term aromatic groups also includes polycyclic ring systems having two or more rings in which two carbons are common to two adjoining rings (the rings are xe2x80x9cfusedxe2x80x9d) wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls.
All value ranges, for example those given for n and m, are inclusive over the entire range. Thus, a range between 0-4 would include the values 0, 1, 2, 3 and 4.
One embodiment of the present invention pertains to novel 4-thio-coumarin derivatives of the formula I: 
wherein
R1 is selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C6 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
R3 is selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or R3 is a group of the formula
Zxe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 0 and 1, provided that when a=0 then b=0, and when c=0 then d=0;
or R3 may occupy two adjacent positions to form a fused aromatic ring, n is selected from values between 0 and 4;
R5 is selected from hydrogen, lower alkyl, lower alkenyl, lower alkynyl, and lower aralkyl, each of which may be unsubstituted or substituted with one or more substituents selected from halogen, lower alkyl, and lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide; or R5 may be a group of the formula 
wherein
R2 is selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
R4 is selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or R4 is a group of the formula
Zxe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 0 and 1, provided that when a=0 then b=0,
and when c=0 then d=0;
or R4 may occupy two adjacent positions to form a fused aromatic ring, and, m is selected from values between 0 and 4.
It is understood that when n is a value greater than 1, each R3 group may be selected independently. Thus, when more than one R3 group is present, the R3 groups may be selected from any of the stated groups so as to be the same or different. This also holds true for R4 when m has a value of greater than 1, and for any other group or substituent which may be selected independently from among various groups or values.
When Y or Q is an ester or amide functionality, 
the group may be in either available orientation. Thus, for example, when 
then R3 may be chosen from 
When one or more chiral centers are present in the compounds of the present invention, the individual isomers and mixtures thereof (e.g., racemates, etc.) are intended to be encompassed by the formulae depicted herein.
In one embodiment of the invention, the 3-position of the 4-thio substituted coumarin is unsubstituted (R5 is H) giving a compound of the formula III: 
wherein R1, R3 and n are as described above. Table 1 provides representative compounds of the formula III.
In a further embodiment of the invention, the 4-thio substituted coumarin is a compound of the formula X 
wherein R3 is as described for the compound of formula I,
R6 is selected from halogen, halogenated methyl, methoxy, and ethoxy;
R7 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy;
R8 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy, and
R9 is selected from H, halogen, halogenated methyl, methoxy, and ethoxy.
In a prefered embodiment for compounds of the formula X, R7 is hydrogen and R3 is selected from halogen and lower alkoxy. In a further prefered embodiment, when R3, R6, R7, or R8 is a halogen, the halogen is preferably fluorine or chlorine.
In another embodiment of the present invention, the 3-position of the 4-thio substituted coumarin is substituted with a group of the formula: 
resulting in a symmetric or unsymmetric coumarin dimer having the formula (II): 
wherein
R1 and R2 are independently selected from
an unsubstituted or substituted aromatic group, wherein the substituted aromatic group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
a substituted or unsubstituted aralkyl group, wherein the substituted aralkyl group may be substituted with one or more of halogen, hydroxy, lower alkyl, lower alkenyl, lower alkynyl, lower alkoxy, thio-lower alkyl, C1-C8 acyl, lower alkyl ester, amide, and lower alkyl amide;
an unsubstituted or substituted alkyl group, wherein the substituted alkyl group is may be substituted with one or more halogen, hydroxy, and lower alkoxy; and
an unsubstituted or substituted cycloalkyl group, wherein the substituted cycloalkyl group may be substituted with one or more halogen, hydroxy, and lower alkoxy;
each R3 and R4 is independently selected from halogen, hydroxy, amino, lower alkyl, lower alkoxy, lower alkenyl, and lower alkynyl, wherein the lower alkyl, lower alkoxy, lower alkenyl and lower alkynyl may be unsubstituted or may be substituted with one or more of halogen, hydroxy, and lower alkoxy; or is a group of the formula
Zxe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Z is selected from 
a, c and e are independently selected from values from 0 to 10;
b and d are independently selected from 6 and 1, provided that when a=0 then b=0, and when c=0 then d=0;
or R3 or R4 may occupy two adjacent positions to form a fused aromatic ring, n and m are independently selected from values between 0 and 4.
In one embodiment of the invention, the 5-, 6-, 7-, and 8-positions of the 4-thio substituted coumarin dimers are unsubstituted (n and m are 0) giving a compound of the formula IIa: 
wherein R1, R3 and are as described above with respect to formula II. Table 2 provides representative compounds of the formula IIa.
In another aspect of the invention, a synthetic process for the preparation of compounds of the formula I is provided. The inventive process uses mild reaction conditions, which provides a high substituent tolerance. The product is obtained in high yield and high purity. The process of the present invention is illustrated by Scheme I: 
wherein R1 is selected from groups that, in combination with the oxygen atom to which it is attached, forms a good leaving group which can be replaced by the thiol nucleophile. R0 is preferably selected from the group consisting of aryl sulfones (tosyl, etc.) triflate, and polyhalogenated aromatic compounds. A tosyl group is particularly preferred. Preparation of compounds of the formula IV is typically from the corresponding alcohol according to procedures know in the art. For example, compounds of the formula IV may be prepared by treating the corresponding 4-hydroxycoumarin with protective group forming agent (non-limiting example includes p-toluenesulfonyl chloride), and a base in a suitable organic solvent. See Wu, J.; Liao, Y.; Yang, Z., J. Org. Chem. 2001, 66, 3642. 4-Hydroxycoumarins may be purchased from commercial sources or may be prepared by processes known in the art. For the general method for preparing 4-hydroxycoumarins, see (a) Laurin P.; Ferroud, D.; Klich, M.; Dupuis-Hamelin, C.; Mauvais, P.; Lassaigne, P.; Bonnefoy, A. and Musicki, B., Bioorg. Med. Chem. Lett. 1999, 9, 2079-2084. (b) Appendino, G.; Cravotto, G.; Giovenzana, G. B. and Palmisano, G. J., Nat. Prod. 1999, 62, 1627-1631.
The base employed in reaction Scheme I may be chosen from amine bases, hydroxide salts (non-limiting examples include sodium hydroxide and tetraalkylamonium hydroxides), carbonate salts, alkoxide salts (non-limiting examples include sodium methoxide and potassium t-butoxide) and the like. Preferred bases are amine bases, and particularly, the tertiary amines, such as triethylamine. The solvent may be chosen from the organic solvents known in the art that are compatible with the reaction conditions, as would be apparent to one of skill in the art. Suitable solvents may include, but are not limited to, methylene chloride, THF, toluene, dialkylethers, ketones (non-limiting examples include acetone and methyl ethyl ketone), esters (a non-limiting example includes ethyl acetate), alcohols (non-limiting examples include methanol and ethanol), acetonitrile, DMSO, DMF, and mixtures thereof. A preferred solvent is methylene chloride.
The reaction is carried out under mild conditions. Preferably, the reaction is run until completion, as monitored by thin-layer chromatography, HPLC or another comparable method. The reaction temperature is preferably less than about 80xc2x0 C. It is particularly preferred that the reaction be performed at room temperature (about 20-25xc2x0 C.). Additionally the reaction is capable of being performed under an air atmosphere, although inert atmospheres (e.g., nitrogen, argon, etc.) may also be used. Thus, the inventive process is applicable to the preparation of a wide variety of 4-thio substituted coumarin derivatives with diverse substitution patterns. As a result, the inventive process in appropriate for use with the solid-support (solid phase) synthesis of 4-thio substituted coumarin derivatives. Thus, the inventive process provides a method for producing a library of 4-thio substituted coumarin derivatives for biological screening.
In another embodiment of the present invention, coumarin dimers are prepared from a compound of the formula V according to the reaction Scheme II: 
wherein R0, is as defines in Scheme I, and R1, R2, R3, R4, n and m are as defined in Formula II. The compound VI is treated with a thiol, represented by R1SH and/or R2SH, and a base in an appropriate solvent. The base, solvent and reaction conditions are as described above for Scheme I.
As shown in Scheme II, when R1 is the same as R2, the reaction of the compound of the formula V with a thiol and base to give the product II can be carried out in a single reaction step. In another embodiment of the invention, when R1 is not the same as R2, the substitution may be carried out in two steps. Short reaction times, even in the presence of excess thiol, generally results in the mono-substituted product (VI). Longer reaction times in the presence of two or more equivalents of thiol results in the final product (II).
In one embodiment, a compound linked to a solid support, represented by the formula VII, is treated according to the process of reaction Scheme I with a thiol and a base in an appropriate solvent. The product of the substitution reaction, represented by the formula VIII, is cleaved from the solid support. This embodiment is summarized in reaction Scheme III: 
wherein R0 is as defined for Scheme I, and R1, R3 and R5 are as defined above for the compound of Formula I,
p is selected from values between 0 and 3.
Xxe2x80x2 is a selected from O, S, xe2x80x94Oxe2x80x94lower alkyl- or a group of the formula
Zxe2x80x2xe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94
wherein Y and Q are independently selected from an aromatic group, O, S, xe2x80x94CRxe2x95x90CRxe2x80x94, 
each R is independently selected from H or lower alkyl,
Zxe2x80x2 is selected from 
a, c and e are independently selected from values from 0 to 10; and
b and d are independently selected from 0 and 1, provided that when a=0 then b=0, and when c=0 then d=0.
X is the chemical group that results from the cleavage of Xxe2x80x2 and linker. Thus, for example, if Xxe2x80x2 is O, then X may be HOxe2x80x94 after cleavage, and if Xxe2x80x2 is xe2x80x94Oxe2x80x94lower alkyl-, then X may be HOxe2x80x94 lower alkyl after cleavage. More generally, when Xxe2x80x2 is selected from a group of the formula Zxe2x80x2xe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94, then X may be a group of the formula HZxe2x80x2xe2x80x94(CH2)axe2x80x94Ybxe2x80x94(CH2)cxe2x80x94Qdxe2x80x94(CH2)exe2x80x94.
The solid support is an insoluble, functionalized, polymeric material to which library members or reagents may be attached via a linker, allowing them to be readily separated (by filtration, centrifugation, etc.) from excess reagents, soluble reaction by-products, or solvents. The solid support is chosen from the solid support materials known in the art, e.g., commercially available resins used for solid phase synthesis in combinatorial chemistry or in solid phase peptide synthesis. For example, the solid support may be chosen from cross-linked polystyrene resins, polystyrene/DVB-polyethylene resins (for example, TentaGel resin, ArgoGel, etc.), controlled-pore glass and Kieselguhr/polyacrylamide. A preferred solid support is a high-capacity polystyrene macrobead.
The linker is a chemical moiety that provides a means of attachment for the immobilized chemical reagent to the solid support. The linker may be any chemical component capable of being selectively cleaved to release a compound of the formula IX from the solid support. Yields for the loading and cleavage to the linker should be as quantitative as possible. The linker may be chosen from those customarily used in the art that are stable to the reactions conditions. Examples of suitable linkers may be found in the review by Guillier et al., Chem. Rev. 2000, 100, 2019-2157. Preferred linkers are silyl based linkers, for example the silyl based linkers disclosed in Sternson et al., J. Am. Chem. Soc. 2001, 123, 1740-1747, Blackwell et al., Org. Lett. 2001, 3, 1185-1188, Pelish et al., J. Am. Chem. Soc. 2001, 123, 6740-6741, and Tallarico et al., J. Comb. Chem. 2001, 3, 312-318, and the like.
A preferred method of generating a 4-thio substituted coumarin library using the process of the present invention is to employ silyl linker-based high capacity macrobeads as a solid support in order to realize a xe2x80x9cone bead, one compoundxe2x80x9d concept. These beads have a high-capacity (up to about 4 mmol/g) and provide sufficient material from a single bead for multiple assays. The silyl linker allows compounds generated on the beads to be released utilizing volatile cleavage reagents (such as HF/pyridine or trimethylsilyl-methanol) so that the compounds can go directly into biological assays without further purification. The purity of the products, as determined by LC-MS, is very high, often exceeding 90%, and in some cases  greater than 99% purity was obtained.
It may be advantageous to employ a temporary protecting group in achieving the final product. The phrase xe2x80x9cprotecting groupxe2x80x9d as used herein means temporary modifications of a potentially reactive functional group which protect it from undesired chemical transformations. Examples of such protecting groups include esters of carboxylic acids, silyl ethers of alcohols, and acetals and ketals of aldehydes and ketones, respectively. The field of protecting group chemistry has been reviewed (Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 2nd ed.; Wiley: New York, 1991).